Method and device for combustion with pulsed fuel split

ABSTRACT

A method of operating a control unit for controlling at least two different input fuel flows to a combustion device, e.g. a gas turbine includes the step of determining on the basis of at least one operating parameter whether the combustion device is in a predefined operating stage. In response hereto, generating a control signal configured for setting a ratio of at least two different input fuel flows to a predetermined value (psc 1,  psc 3 ) for a predetermined time (dt) in case the combustion device is in the predefined operating stage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US Divisional Application of US National StageApplication 13/879,056, filed Apr. 12, 2013 of International ApplicationNo. PCT/EP2011/067172, filed Sep. 30, 2011 and claims the benefitthereof. The International Application claims the benefits of Europeanapplication No. 10187429.5 filed Oct. 13, 2010. All of the applicationsare incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present invention relates to the field of combustion devices and inparticular to combustion devices in the form of gas turbines.

BACKGROUND OF INVENTION

WO 2007/082608 A1 relates to a control arrangement which detects atemperature sensor output and, depending on that sensor output, variesthe fuel supplies within the burner in such a way as to maintain thetemperature of a component part below a maximum value, while keeping thefuel in incoming fuel supply line substantially constant.

In view of the above-described situation, there exists a need for animproved technique that enables to provide a combustion device, whilesubstantially avoiding or at least reducing one or more problems ofknown systems.

SUMMARY OF INVENTION

This need may be met by the subject matter according to the independentclaims. Advantageous embodiments of the herein disclosed subject matterare described by the dependent claims.

According to a first aspect of the invention there is provided acombustion device control unit comprising (i) a control input forreceiving at least one operating parameter indicative of the operationof a combustion device; (ii) a control output for outputting a controlsignal for controlling at least two different input fuel flows to thecombustion device; (iii) wherein the control unit is configured fordetermining on the basis of the at least one operating parameter whetherthe combustion device is in a predefined operating stage; (iv) andwherein the control unit is further configured for generating thecontrol signal so as to set the ratio of the at least two differentinput fuel flows to a predetermined value for a predetermined time incase the combustion device is in the predefined operating stage.

This aspect of the invention is based on the findings of the inventorsthat by setting the ratio of the at least two different input fuel flowsto a predetermined value for a predetermined time surprisingly resultsin a “smoother” operation of the combustion device compared to knowncontrol algorithms and can reduce a temporary increase or overshoot ofnitrogen oxide (NOx) emissions. Generally herein NOx stands for oxidesof nitrogen as the chemical compounds NO and NO₂.

According to an embodiment, the combustion device is a gas turbine or isa combustor comprised in a gas turbine engine. According to a furtherembodiment, the combustion device control unit is a gas turbine controlunit.

According to a further embodiment, the predetermined value and thepredetermined time are initially defined during manufacturing of thecombustion device. According to an embodiment, the definition of thepredetermined value and the predetermined time are unchangeable duringoperation of the combustion device.

According to a further embodiment, the definition of the predeterminedvalue and the predetermined time are changeable in a service mode of thecombustion device, wherein the definition of the predetermined value andthe predetermined time is altered depending on the actual operatingconditions, e.g. depending on the fuel used for the combustion device.It should be noted that herein the term “predetermined value” is notlimited to a specific value but also includes relative settings, e.g.increasing an actual value by a specific, predetermined percentage.

According to an embodiment, setting the ratio of the at least twodifferent input fuel flows to a predetermined value comprises changingthe ratio of the at least two different input fuel flows from a presentvalue to the predetermined value in a stepwise manner. However, itshould be understood that changing the ratio of the at least twodifferent input fuel flows in a stepwise manner still means that thecontrol signal is generated within the operating limits of thecombustion device control unit and that the ratio of the at least twodifferent input fuel flows is changed within the operating limits of thecombustion device to which the control unit is operatively connected. Inother words, according to an embodiment “stepwise” means “as fast aspossible within operating limits”. Anyway, “stepwise” is not to beinterpreted in a mathematical sense but rather in a technical sense.

According to another embodiment, setting the ratio of the at least twodifferent input fuel flows to a predetermined value for a predeterminedtime is part of a pulse shaped temporal change of the ratio of the atleast two different input fuel flows, referred to as fuel ratio pulse inthe following. According to an embodiment, the pulse shaped temporalchange of the ratio of the at least two different input fuel flows has apredetermined pulse height and predetermined pulse width. Herein, thesetting of the ratio of the at least two different input fuel flows to apredetermined value corresponds to a rising pulse edge of the fuel ratiopulse. According to an embodiment, also the falling pulse edge of thefuel ratio pulse is generated by setting the ratio of the at least twodifferent input fuel flows from the predetermined value to a targetvalue. In such a case of a square pulse, the pulse width corresponds tothe predetermined time.

According to an embodiment, after the predetermined time the ratio ofthe at least two different input fuel flows is set to a value thatcorresponds to a control regime applied before setting the ratio of theat least two different input fuel flows to a predetermined value. Forexample, in an embodiment, the combustion device is controlled accordingto a control regime (i.e. a control method). Upon a disturbance leadingto the predefined operating stage, a fuel ratio pulse is applied,wherein the ratio of the at least two different input fuel flows are setto a predetermined value for a predetermined time, and wherein after thefuel ratio pulse, e.g. after the predetermined time, the fuel ratio isagain determined by the control regime. According to an embodiment, thetarget value of the fuel ratio pulse corresponds to a control regimeapplied before setting the ratio of the at least two different inputfuel flows to a predetermined value.

According to an embodiment, the output signal provided by the controlunit changes qualitatively in the same manner as the fuel flow ratio,e.g. in a step wise manner, in a pulsed manner, or according to anyother embodiment of the herein disclosed subject matter, if it isdetermined that the combustion device is in the predefined operatingstage.

According to an embodiment of the herein disclosed subject matter, theat least two different input fuel flows include (a) a main fuel flow toa main combustion region of a combustor of the combustion device; and(b) a pilot fuel flow to a pilot region of the combustor of thecombustion device. In an embodiment, the main fuel flow generallydetermines the actual power of the combustion device, whereas the pilotfuel flow is used for stabilizing the flame in the combustor generatedby the main fuel flow. According to an embodiment, the combustion devicecomprises a single combustor. According to other embodiments, thecombustion device comprises two or more combustors.

According to an embodiment, the at least one operating parameterincludes at least one of a temperature and a pressure. To this end,respective sensors for sensing the at least one operating parameter maybe provided. The temperature may be a temperature of a part of thecombustor. According to another embodiment, the temperature is atemperature of the combustion device. For example, in case thecombustion device is a gas turbine, the temperature may be thetemperature of an exhaust gas of the gas turbine. According to a furtherembodiment, the pressure is a pressure in the combustor of a combustiondevice.

According to a second aspect of the herein disclosed subject matter, acombustion device is provided, the combustion device comprising (i) acombustor; (ii) a combustion device control unit according to the firstaspect or an embodiment thereof

According to an embodiment, the at least one sensor for sensing the atleast one operating parameter is part of the combustion device whichincludes the combustor and the combustion device control unit.

According to a further embodiment of the herein disclosed subjectmatter, the combustion device further comprises a fuel split device forcontrollably splitting a supply fuel flow into the at least twodifferent input fuel flows to the combustor, e.g., in an embodiment,into the main fuel flow and the pilot fuel flow disclosed herein. A fuelsplit device comprises the advantage that the overall fuel supply to thecombustion device is determined by the supply fuel flow and that theratio of the at least two different input fuel flows is independentlyadjustable with the fuel split device. According to other embodiments,the at least two different fuel flows are provided by some othersuitable supply arrangement.

According to a third aspect of the herein disclosed subject matter, amethod of operating a combustion device control unit configured forcontrolling at least two different input fuel flows to a combustor isprovided, the method comprising: (i) determining on the basis of atleast one operating parameter whether a the combustion device is in apredefined operating stage; (ii) generating a control signal configuredfor setting a ratio of the at least two different input fuel flows to apredetermined value for a predetermined time in case the combustiondevice is in the predefined operating stage.

According to embodiments of the third aspect, the control signal isconfigured as disclosed with regard to the first aspect or an embodimentthereof. According to further embodiments of the third aspect, thecontrol signal is configured in accordance with the second aspect or anembodiment thereof.

According to embodiments of the third aspect, the control signal isconfigured so as to set the fuel ratio of the at least two differentfuel flows as disclosed with regard to the first aspect or an embodimentthereof. According to further embodiments of the third aspect, thecontrol signal is configured so as to set the fuel ratio of the at leasttwo different fuel flows in accordance with the second aspect or anembodiment thereof.

According to a fourth aspect of the herein disclosed subject matter, acomputer program for generating a control signal is provided, thecomputer program, when executed by a data processor, is adapted forcontrolling the method according to the third aspect or an embodimentthereof.

As used herein, reference to a “computer program” is intended to beequivalent to a reference to a program element and/or a computerreadable medium containing instructions for controlling a computersystem to coordinate the performance of the above described method.

The computer program may be implemented as computer readable instructioncode by use of any suitable programming language, such as, for example,JAVA, C++, and may be stored on a computer-readable medium (removabledisk, volatile or non-volatile memory, embedded memory/processor, etc.).The instruction code is operable to program a computer or any otherprogrammable device to carry out the intended functions. The computerprogram may be available from a network, such as the World Wide Web,from which it may be downloaded.

According to an embodiment, the computer program is provided in the formof a full release. According to other embodiments, the computer programis provided in the form of a software update which requires a previousinstallation that is updated to provide the functionality according toaspects and embodiments of the herein disclosed subject matter.

The invention may be realized by means of a computer programrespectively software. However, the invention may also be realized bymeans of one or more specific electronic circuits respectively hardware.Furthermore, the invention may also be realized in a hybrid form, i.e.in a combination of software modules and hardware modules.

In the above there have been described and in the following there willbe described exemplary embodiments of the subject matter disclosedherein with reference to a combustion device control unit and a methodof operating a combustion device control unit. It has to be pointed outthat of course any combination of features relating to different aspectsof the herein disclosed subject matter is also possible. In particular,some embodiments have been described with reference to apparatus typeclaims whereas other embodiments have been described with reference tomethod type claims. However, a person skilled in the art will gatherfrom the above and the following description that, unless othernotified, in addition to any combination of features belonging to oneaspect also any combination between features relating to differentaspects or embodiments, for example even between features of theapparatus type claims and features of the method type claims isconsidered to be disclosed with this application.

The aspects and embodiments defined above and further aspects andembodiments of the present invention are apparent from the examples tobe described hereinafter and are explained with reference to thedrawings, but to which the invention is not limited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a cross section of a part of a combustiondevice according to embodiments of the herein disclosed subject matter.

FIG. 2 schematically illustrates sets of operating parameterscorresponding to predefined operating stages according to embodiments ofthe herein disclosed subject matter.

FIG. 3 illustrates the setting of the ratio of the two different inputfuel flows to a predetermined value for a predetermined time accordingto embodiments of the herein disclosed subject matter.

DETAILED DESCRIPTION OF INVENTION

The illustration in the drawings is schematic. It is noted that indifferent figures, similar or identical elements are provided with thesame reference signs or with reference signs, which are different fromthe corresponding reference signs only within the first digit.

In the drawings, embodiments of the herein disclosed subject matter aredescribed with reference to a combustion device in the form of a gasturbine. However, other types of combustion devices are also possible.

FIG. 1 schematically shows a part of a combustor 10 of a combustiondevice 1 according to embodiments of the herein disclosed subjectmatter. According to an embodiment, the combustor 10 comprises afront-end 20, a swirler 21, a burner pre-chamber 22 and a combustionvolume 23. A main fuel flow is introduced into the swirler 21 by way ofthe front-end part 20 through a conduit 24. A pilot fuel flow enters theburner space through a conduit 25.

The main and pilot fuel-flows are provided by a fuel split device 26 forcontrollably splitting a supply fuel flow, provided via a supply conduit27, into the main fuel flow and the pilot fuel flow. The fuel splitdevice includes one or more valves in one embodiment. The supply fuelflow represents the total fuel supply to the combustor 10. A combustiondevice control unit 36 (e.g. a gas turbine control unit, hereinafterreferred to as control unit) is provided for controlling the fuel splitdevice 26.

The main fuel flow enters the swirler 21 through a main inlet 28, fromwhere it is guided along swirler vanes (not shown in FIG. 1) and mixedwith incoming compressed air fed to the swirler 21. According to anembodiment, the main inlet 28 includes a set of main fuel nozzles orinjector nozzles. Downstream the swirler 21, the fuel-air mixture entersthe burner pre-chamber 22.

The pilot fuel flow enters the burner pre-chamber 22 via a pilot fuelinlet 29 provided at the end of the conduit 25. The pilot fuel inlet 29may include a single injection nozzle or a single hole in one embodimentor, according to another embodiment, a plurality of injection nozzles orholes.

The resulting air-fuel mixture maintains a burner flame 30. The hot airfrom this flame enters the combustion volume 23.

According to an embodiment, one or more sensors for sensing at least oneoperating parameter are provided. According to an embodiment shown inFIG. 1, temperature and pressure are operating parameters in the senseof the herein disclosed subject matter. To this end, a temperaturesensor 32 is provided for measuring a temperature of the combustor 10and a pressure sensor 33 is provided for measuring a pressure of thecombustor 10. According to an embodiment, the temperature sensor 32 islocated on a life-critical part of the combustor, e.g. on acircumferential wall 31 defining the combustion volume 23. According toa further embodiment, the pressure sensor 33 is located within thecombustion volume 23.

The output of the temperature sensor 32, providing temperatureinformation 34, and the output of the pressure sensor 33, providingpressure information 35, are fed to the control unit 36. As a furtherinput to the control unit 36 a load information 38 is provided. The loadinformation 38 may represent in respective embodiments a speed or apower output of a driven generator which may be connected to the shaftand driven by the shaft of the gas turbine, generated power by thedriven generator, a rotational speed of a shaft of the gas turbine, or atorque provided by the shaft. According to another embodiment, the loadinformation may also represent the mass flow exiting the combustionchamber. It may be taken from a sensor (not shown in FIG. 1) or may bederived from a further operating parameter. According to anotherembodiment, the load information 38 includes a combination of loadinformation of two or more of the above mentioned embodiments.

According to an embodiment, the control unit 36 has a control input 100a, 100 b, 100 c for receiving at least one operating parameterindicative of the operation of a gas turbine. For the combustor 10 shownin FIG. 1 the control unit receives the operating parameters temperatureinformation 34, pressure information 35 and load information 38.

It should be noted that these exemplary parameters are used forillustrative purposes only and that according to other embodiments otheroperating parameter, a subset of the exemplary operating parameters oradditional operating parameters may be used by the control unit 36.

The control unit 36 further comprises a control output 102 foroutputting a control signal 37 for controlling at least two differentinput fuel flows, e.g. the main fuel flow and the pilot fuel flow in theillustrated embodiment, to the combustor.

According to an embodiment, the control unit 36 comprises adetermination unit 36 a for determining whether the gas turbine is inthe predefined operating stage. According to an embodiment, thedetermination unit 36 a is configured for providing an output,indicating whether the gas turbine is in the predefined operating stage,on the basis of the output signal of the at least one sensor. Accordingto a further embodiment, the gas turbine control unit comprises acontrol signal generation unit 36 b for generating the control signal37. According to an embodiment the control signal generation unit 36 bis configured for generating the output signal depending on the outputof the determination unit 36 a.

In accordance with further embodiments, the control unit 36 isconfigured for generating the control signal 37 so as to set the ratioof the at least two different input fuel flows to a predetermined valuefor a predetermined time in case the gas turbine is in the predefinedoperating stage. According to an embodiment, the fuel split device 26sets, in response to the control signal 37, the ratio of the main fuelflow and the pilot fuel flow to the predetermined value.

In accordance with embodiments of the herein disclosed subject matter,the control unit 36 is configured for determining on the basis of the atleast one operating parameter whether the gas turbine is in a predefinedoperating stage. For example, the predefined operating stage may be anoperating stage of high temperature above a temperature threshold.According to another embodiment, the predefined operating stage is anoperating stage of high amplitude (above an amplitude threshold) ofdynamic pressure oscillations in the combustion area of the combustor.According to other embodiments, a combination of operating parameters isused for determining whether the gas turbine is in a predefinedoperating stage.

FIG. 2 schematically illustrates sets of operating parameterscorresponding to predefined operating stages according to embodiments ofthe herein disclosed subject matter. FIG. 2 is a graph of main/pilotfuel split over the load of the gas turbine. The horizontal axisrepresents low loads of the gas turbine on the left hand side and highloads on the right hand side. The vertical axis represents a fuel splitwith a higher amount of the pilot fuel flow at the upper range of thevertical axis and less pilot fuel flow at the lower range of thevertical axis. The vertical axis does not show absolute values of fuelsupply but the relative value of the pilot fuel supply in comparison tomain fuel supply.

According to an embodiment, the hatched area referenced as A in FIG. 2represents a set of operating conditions in which a component part of acombustor is in danger of suffering damage due to overheating. Forexample there may be conditions in which a specific main fuel flow topilot fuel flow split will result in overheating of a combustor surfacefor a given load. According to embodiments of the herein disclosedsubject matter, the control unit 36 is configured for providing anoutput signal 37 (see FIG. 1) so as to effect, for a given load, adivision (split) between the main fuel flow and pilot fuel flow suchthat area A is avoided.

According to other embodiments, the control unit 36 is configured forproviding an output signal 37 so as effect a ratio between the main fuelflow and the pilot fuel flow such that area B is avoided. According toan embodiment, the area B represents a set of operating conditions inwhich the amplitude of dynamic pressure oscillations in the combustionarea is undesirably high. When such dynamic pressure oscillations exceedacceptable levels, the operation of the gas turbine and/or themechanical longevity of the combustion system can be severely impacted.

Hence it is desirable also to be able to keep away from area B as wellas from area A. This is realised according to embodiments of the hereindisclosed subject matter.

FIG. 3 illustrates the setting of the ratio of the two different inputfuel flows (main fuel flow and pilot fuel flow) to a predetermined valuefor a predetermined time according to embodiments of the hereindisclosed subject matter. In particular, FIG. 3 shows a correction to abasic value of a pilot split, i.e. of the ratio between the main fuelflow and the pilot fuel flow the over time t in seconds. In FIG. 3 thevertical axis represents a fuel split with a higher amount of pilot fuelflow at the upper range of the vertical axis and less pilot fuel flow atthe lower range of the vertical axis. The basic value of the pilotcorresponds to a correction of 0% in FIG. 3. According to an embodiment,the basic value of the main fuel flow to pilot fuel flow ratio is aninitial value that has been determined and set during manufacturing ofthe gas turbine. The correction to this initial value may be performedaccording to any suitable method or algorithm, e.g. on the basis ofoperating conditions, e.g. the load of the gas turbine. Such a method isreferred to as a control regime for normal operation in the followingand is not subject of the herein disclosed subject matter. For examplethe control regime for normal operation may include varying the ratio ofthe two different input fuel flows (main fuel flow and pilot fuel flow)depending on the load of the gas turbine, e.g. according to apre-defined fuel split map. However, if the predefined operatingcondition is determined, the control regime for normal operation is nolonger applied. Rather, according to an embodiment of the hereindisclosed subject matter, the ratio of the main fuel flow and the pilotfuel flow is set to the predetermined value for the predetermined time.

According to an embodiment, except for the predetermined time withinwhich the ratio of the main fuel flow and the pilot fuel flow is set tothe predetermined value, the ratio of these different input fuel flowsis set to a value that corresponds to the control regime employed fornormal operation of the gas turbine. However, in case a predefinedoperating stage is reached the ratio is set to the predetermined valuefor the predetermined time according to embodiments of the hereindisclosed subject matter. Thereafter, the ratio is again set to a valuethat corresponds to the control regime for normal operation.

As shown in the exemplary scenario in FIG. 3, from t=t0 to t=t1 thecontrol unit 36 (see FIG. 1) adjusts the correction to the pilot splitaccording to the control regime for normal operation. At t=t1 thecontrol unit 36 determines that the gas turbine is in a predefinedoperating stage. The ratio between the main fuel flow and the pilot fuelflow at this time is psc0. In accordance with embodiments of the hereindisclosed subject matter, the control unit 36 sets the correction to thepilot split such that the ratio of the main fuel flow and the pilot fuelflow equals a predetermined value. According to an embodiment shown inFIG. 3, setting the ratio to a predetermined value corresponds toincreasing the actual ratio (i.e. the ratio before increasing it to thepredetermined value) by a predetermined percentage. For example,according to an embodiment, the predetermined value is obtained byincreasing the pilot fuel flow over the main fuel flow so as to achievean increase of the actual ratio in a range of 0.1% to 1%. According to afurther embodiment, the predetermined time is in a range between 0.5second and 15 seconds. It should be understood that the predeterminedvalues differ for different types of combustion devices. According toother embodiment, the predetermined value is obtained by increasing theactual ratio by a fixed amount. According to an embodiment, thepredetermined percentage or the fixed amount, respectively, aredetermined based on measurements or operating conditions, e.g. the fuelused, etc. However any other method of determining the predeterminedvalue of the ratio between the main fuel flow and the pilot fuel flow isalso possible.

Having now again regard to FIG. 3, the predetermined value of the ratiobetween the main fuel flow and the pilot fuel flow, corresponding to apilot split correction of psc1, is maintained for the predetermined timedt. Then, at t2=t1+dt the control regime for normal operation is used todetermine the pilot split correction value psc2 for the actual operatingconditions of the gas turbine at t=t2. As is apparent from FIG. 3,setting the ratio between the main fuel flow and the pilot fuel flow tothe predetermined value for the predetermined time and setting the ratiobetween the main fuel flow and the pilot fuel flow to a valuecorresponding to the control regime for normal operation at t=t2 resultsin a fuel flow ratio pulse 200 having a pulse width of dt=t2−t1 and apulse height of dh=psc1−psc0. Generally herein, the pulse height isdefined by the predetermined value, i.e. by the rising flank of the fuelflow ratio pulse.

Between t=t2 and t=t3, the pilot split correction is determined by thecontrol regime for normal operation. At t=t3 a predefined operatingcondition occurs. As a result, the control unit 36 again sets the ratiobetween the main fuel flow and the pilot fuel flow to a predeterminedvalue psc3 and maintains this value for the predetermined time dt. Fromt=t4 on, again the ratio between the main fuel flow and the pilot fuelflow is determined by the control regime for normal operation.

According to an embodiment shown in FIG. 3, the predetermined time dt isthe same for all occurrences of the predefined operating condition.According to other embodiments, the predetermined time dt depends on oneor more operating parameters of the gas turbine.

A gas turbine usually comprises a number of such combustors, e.g. of thetype shown in FIG. 1. In case the combustion device comprises two ormore combustors, according to an embodiment the main and pilot fuel-flowdistribution will be the same for a subset or for all of thesecombustors. According to other embodiments, each combustor isindividually controlled regarding its ratio between the main fuel flowand the pilot fuel flow.

It is a common problem that, due to the high temperatures generatedinside such combustors, various component parts of the combustors runthe risk of overheating, which can seriously damage the combustor, or atleast impair its performance. Also NOx emissions are a major concern. Itis an aim of embodiments of the herein disclosed subject matter toprovide a combustion apparatus which reduces the risk of suchoverheating and is directed to create only low emissions at a wide rangeof operation.

According to embodiments of the invention, any component of the gasturbine control unit, e.g. the determination unit or the control signalgeneration unit are provided in the form of respective computer programproducts which enable a processor to provide the functionality of therespective elements as disclosed herein. According to other embodiments,any component of the gas turbine control unit, e.g. the determinationunit or the control signal generation unit may be provided in hardware.According to other—mixed—embodiments, some components may be provided insoftware while other components are provided in hardware. Further, itshould be noted that a separate component (e.g. module) may be providedfor each of the functions disclosed herein. According to otherembodiments, at least one component (e.g. a module) is configured forproviding two or more functions as disclosed herein.

It should be noted that the term “comprising” does not exclude otherelements or steps and the “a” or “an” does not exclude a plurality. Alsoelements described in association with different embodiments may becombined. It should also be noted that reference signs in the claimsshould not be construed as limiting the scope of the claims.

In order to recapitulate the above described embodiments of the presentinvention one can state:

It is described a combustion device control unit and a combustiondevice, e.g. a gas turbine, which determine on the basis of at least oneoperating parameter whether a the combustion device is in a predefinedoperating stage. In response hereto, a there is generated a controlsignal configured for setting a ratio of at least two different inputfuel flows to a predetermined value for a predetermined time in case thecombustion device is in the predefined operating stage.

What is claimed is:
 1. A method for operating a control unit forcontrolling at least two different input fuel flows to a combustiondevice, comprising: receiving at least one operating parameter through acontrol input of the control unit; determining whether the combustiondevice is operated in a predefined operating stage based on the at leastone operating parameter; and generating a control signal for setting aratio of the at least two different input fuel flows to a predeterminedvalue for a predetermined time in case the combustion device is in thepredefined operating stage, wherein the ratio of the at least twodifferent input fuel flows is set to the predetermined value by changingthe ratio of the at least two different input fuel flows from a presentvalue to the predetermined value in a stepwise manner, and wherein theratio of the at least two different input fuel flows is set to thepredetermined value for the predetermined time comprising a pulse shapedtemporal change of the ratio of the at least two different input fuelflows.
 2. The method according to claim 1, wherein after thepredetermined time the ratio of the at least two different input fuelflows is set to a value that corresponds to a control regime appliedbefore setting the ratio of the at least two different input fuel flowsto the predetermined value.
 3. The method according to claim 1, whereinthe at least two different input fuel flows include: a main fuel flow toa main combustion region of a combustor of the combustion device; and apilot fuel flow to a pilot region of the combustor of the combustiondevice.
 4. The method according to claim 1, wherein the at least oneoperating parameter comprises at least one of a temperature and apressure.
 5. The method according to claim 1, further comprising thestep of controllably splitting a supply fuel flow into the at least twodifferent input fuel flows to a combustor through the generated controlsignal sent to a fuel split device.
 6. The method according to claim 1,wherein the combustion device comprises two or more combustors.
 7. Themethod according to claim 6, wherein the at least two different inputfuel flows distributions are the same for all of the combustors.
 8. Themethod according to claim 6, wherein each combustor is individuallycontrolled regarding its ratio between each of the at least twodifferent input fuel flows.
 9. A computer readable medium, comprising: acomputer program stored in a computer readable medium for controlling atleast two different input fuel flows to a combustion device, wherein thecomputer program is executed by a data processor to perform a method asclaimed in claim 1.